Micro Moog Story...

[sweetbeats]

Well this is just a great success story...my brother and I got this moog working 100%...and with some selective resistor upgrades, and a conservative upgrade to the output amp (TL072 equivalent), the noise floor is SUPER low...

The last remaining issue was the Sample & Hold circuit, and those of you that know this family of devices know it is its crown jewel. Since my brother has owned this thing (like since 1978 or thereabouts), the Sample & Hold circuit has never worked, and he's taken it to a couple techs over the years to try and fix it to no avail; a real bummer.

Because the "transconductor" opamp in the output amplifier circuit was bad, and since there was one of the same parts in the Sample & Hold circuit, we replaced that with a NOS Harris 3080 part. It didn't fix the problem. The service manual also points to the JFET associated with that amp as a possible culprit. We pulled the original part and some basic tests with a multimeter said that was bad too. My brother sourced an NTE467 as a suitable replacement. We put that in, powered it up, and *BAM* right away there was that coool modulated randomization...we knew right away we'd licked it and it was instant high-five. Totally cool to hear what my brother had wanted to hear all these years!

We also serviced the modulation wheel pot and repaired some nearly broken wires and some cold solder joints...my brother serviced the keyboard buss bar and key contacts...

This thing makes the coolest sounds....!

I'll get some sound samples put up at some point.

Here I'm pointing to the transistor and opamp that were replaced to enable the Sample & Hold circuit to work:




And here is a happy brother just moments after success was realized:

 

[sweetbeats]

So this is probably the last installment of this "Story...", as my brother and I busted out the scope and DMM and went through the tuning and calibration procedures in the service manual...and changed a number of the procedures in the service manual in order to get more accurate results. And then a couple days ago my brother installed new key bushings. So the micromoog is recapped, repaired, cosmetically refurbished, and calibrated. The only other things that *might* occur in the future would be to fabricate a new base-board for it out of MDF (the factory particle board base is chewed up a bit), and there's a kit to allow MIDI data to trigger the moog that we might put in later. But for now I believe it is as tip-top as any micromoog out there, and it sounds fantastic...it really does. And the noise floor is shockingly quiet.

Here's a couple sound samples focusing on the Sample & Hold circuit:

https://quay.com/todblog/wp-content/uploads/2014/07/Wandering%20Moog.mp3.php

http://quay.com/todblog/wp-content/uploads/2014/07/Nasty%20Moog.mp3.php

The micromoog has been in a closet or some form of storage for literally decades...soiled and in disrepair. It now sits in my brother's very digital music production room on a perch; "Certainly it cannot go back into the closet...it will get used." says he.

 

[The Ghost of FM]

Good stuff indeed!

God forbid, if you ever lose your "day job", I think you can pretty easily set up a gear refurbishment company!

Cheers!

 

[Steenamaroo]

Great job! Thanks for sharing in such detail.

I especially like the last pic. This 'shelfie' craze is really catching on.

 

[sweetbeats]

Thanks, gents!

It was a fun project from the standpoint it was a departure from anything I've ever worked on, but mainly because it was a collaborative with my brother...lotta history tied up in it...and the results were very satisfying!

Jeff, that's really high praise and I thank you. Really, that would be a dream job, but I fear not very lucrative. 4 kids in braces = $$$!! I suppose it all comes down to business planning and marketing, but I'm not necessarily cut for either of those aspects. I'm a program/operations manager by trade with a coincident background in IT service and support...not much of an entrepreneur, though I did have a fledgling acoustic drum manufacturing and repair company in the mid 90s...but I do love to tinker and refurbish. Just finished going through my Dad's Pioneer RT-909, and am now (finally) riding my 1981 Honda CX500C almost daily after bringing it back from the dead...got it for free...but the "going through it" was way below skin-deep.

Before:



After:



I think people would have to (figuratively speaking) be knocking at my door with refurb job requests before I'd think of doing anything for others (as opposed to going out and looking for business). I realize your comment was maybe somewhat tongue-in-cheek, but it IS something I've thought about, and something I enjoy doing. In the meantime, I'll keep plugging away at the projects I have and sharing the experience with all who care to read...currently taking some more stabs at the Ampex MM-1000, have some wrap-up work on the Tascam M-__ once I can coordinate a visit with my electronics guru friend up in Washington, and then get the 3M-M64 recapped and dialed in, and then out on the horizon is picking back up the MCI JH-416"A" project.